With any new gun run it for a while before trying to do mods. Once you know it is a good running gun, it is a Glock, then night sights are a must for me, just my preference. More ammo, more ammo and again more ammo. A lot of guys will add the extended slide catch(not a slid release here) or the extended mag release, just not my thing. A little color on the slide is always nice to add that personal touch. Grip tape, or stippling if you have a problem holding onto it.
I have had my G22 for several years and the only thing I have done to it is paint the slide, add night sights, buy more mags, feed it all of the ammo I can afford to give it. I did buy a good cleaning kit(I'm anal about my guns being clean) and a nice range bag and hearing protection.